Perhaps because I was never the kid who had the super sized 128-pack of crayons, I never developed much of an artistic eye, especially for colors. Having only the 16-pack, with nary even the free crayon sharpener is something I obviously rue to this day. (Made worse by the fact that, only a few years later, my younger brother got a 64-pack of crayons complete with built-in crayon sharpener. Sigh.)
Anyway, the point is, if anyone needs help with colors, it's me. That's why I love that Office 12 helps me make better looking documents by improving the selection of colors throughout the product.
Now, it is true that many of the core Office 12 products (including Word, Excel, and PowerPoint) support a new model for document themes, which let you change the color scheme, font scheme, and special effects scheme on a per-document basis. Much can and should be written about how all of this works in the future.
But putting that aside for the time being, every document comes with a "default" theme which contains a color scheme full of well-matched colors. The result is that, even if you don't mess with the new theme or color scheme features at all, your documents look modern and well-matched. (Of course, it doesn't hurt that all of the default object styles in the contextual tab galleries will be based on these colors as well--so when you put a chart or table in, all of the styles you can choose between will match by default.)
In general, Office programs started out by supporting 16 colors. These were the standard "Windows 16-color palette" colors, and they're formed by trying out various combinations of 0, 128, and 255 as red, blue, and green amounts. For instance, RGB(0, 0, 0) is black, RGB(255, 0, 0) is bright red, and RGB(0, 255, 255) is bright teal (a mix between full blue and full green.)
As the Office programs continued to improve, certain programs were upgraded to 32 or even 64 colors in their color picker. These were still generated based on binary mathematical principles instead of on aesthetic design principles, but at least if you allowed some of the RGB values to be 64 or 32, you could get a wider range of colors. And, of course, in recent versions of Office you could always bypass the color picker and choose from any possible color--but this was a one-off selection and did not make choosing matching colors easy unless you are a graphics designer.
The new Office color gallery has two parts: the top half contains 10 fully saturated colors (meaning as bright as possible) and then a number of less saturated variants. The colors have been selected to look good together, and many of the default styles in Office use gradients between a lighter and darker variant within a color column. The bottom half of the color picker contains 10 "standard" colors that don't change based on the color scheme. Here you have a true red, a bright yellow and green that you can use, for instance, to mark up a spreadsheet with good values green and bad values red.
The Office 12 Beta 1 Color Gallery showing the default color scheme
Just as always, whenever possible you can choose to bypass the color gallery altogether and choose from any of the 16.7 million colors supported by Office.
But using the color gallery ensures that the objects in your documents match and helps you choose colors that look a lot better than the "computer colors" brought to the foreground by old-school Office. And, it makes it a lot easier to choose colors for gradients and shadows by going up and down the column of matching tints and shades.
There's a lot more to write about the Office 12 themes and color schemes story, but this gives you a small glimpse of how the products work even if you don't explicitly use these new features.